This invention relates to a system for controlling the operation of a hydraulically actuated device such as a hydraulic motor. The control system according to the invention has particular utility in conjunction with the hydraulic drive motor of the vibrator in a self-propelled vibratory compactor of the roll type, but with no unnecessary limitations thereto being intended.
As is well known, vibratory roller compactors combine static weight with vibratory forces for dynamic compaction of soils, asphalt or the like. Such compactors have the problem that if the vibrator mounted within their roll is held in motion while the vehicle is at rest, a depression is formed in the soil or asphalt surface just under the roll. Hence, as the compactor travels back and forth over a limited area of desired soil or the like to be compacted, for example, depressions are formed at the opposite ends of the area where the vehicle temporarily stops for a change of direction.
In order to overcome this problem, it has been suggested to provide a selector valve for the on-off control of communication between the hydraulic drive motor of the vibrator and a fixed displacement pump supplying pressurized fluid thereto. The selector valve is adapted to be closed automatically to block communication between pump and motor when the vehicle is at rest or travelling very slowly.
This prior art control system has the disadvantage, however, that the selector valve in use must be a high pressure, large capacity valve since it is required to open and close the main supply circuit connecting the fixed displacement pump to the vibrator motor. Moreover, the main supply circuit suffers considerable shock each time the valve is opened or closed, and there is a substantial amount of energy wasted particularly when the vibrator is set out of operation.